Not Applicable.
This invention relates to a detection system for sensing an object in motion relative to a container, especially tubular in design, whereby at least one magnetic unit is associated with the container and or object, generating as well as measuring magnetic fields, and at least one evaluation device is connected to the magnetic units and serves to receive sensing signals from the magnetic units.
A detection system of this type is described in U.S. Pat. No. 3,103,976. That particular detection system is used in locating pipes, and especially pipe ends to be joined, in underwater drilling and similar operations. A guide tube, serving as a container extending between a topside derrick and a frame section anchored on the sea bottom, is equipped on its outside with a coil as the magnetic unit generating a magnetic field and with each two search coils respectively mounted above and below the first coil and serving as the magnetic-field measuring magnets. Electric cables connect these various coils with a topside evaluation unit within the derrick. The magnetic-held-generating coil produces a magnetic field inside the guide tube essentially along the longitudinal axis of the tube. That magnetic field also permeates the two magnetic-field-measuring coils. If and when within the guide tube a drill rod, tool, pipe or the like is shifted, the magnetic field in these measuring coils will change as a function of the position of the moving object, leading to a corresponding induction in these coils. It is thus possible to determine when the object concerned has reached one of these magnetic-field-measuring coils or for instance the blowout valve located on the sea bottom.
That earlier detection system, however, is essentially limited to sensing the position only of the forward end of the moving object, with the positional detection accuracy being determined by its distance from the coils which are mounted along the longitudinal axis of the guide tube, by the coil width in the longitudinal direction, and similar factors.
It is the objective of this invention to provide an improved detection system of the type first above mentioned, the improvement consisting in the ability, in simple fashion and with a relatively high degree of accuracy, to determine not only the position of the object relative to the container in the longitudinal direction but also its position in the transverse direction relative to the container.
In conjunction with the characteristic features specified within the main concept of the claims, this is accomplished in that the magnetic units produce a maximum magnetic flux essentially perpendicular to the direction of relative movement between the object and the container. This causes a change in the magnetic field and in the magnetic flux when the object is close enough to the container that both are located within the magnetic field of the magnetic-field-generating magnetic unit. At the same time, given this position of the object and the container relative to each other, there will be a change in the magnetic field in the direction perpendicular to the relative movement, thus yielding for the evaluation device additional information on the position of the object and the container perpendicular to the direction of relative movement.
According to this invention, the functionality of the detection system does not depend on whether the container, for instance tubular in design, is stationary while the object moves relative to it, or vice versa, for as long as at least the moving part contains a magnetic element which triggers a corresponding change in the magnetic field between the magnetic units.
In oil-drilling or similar operations, it may be advantageous in this context if in particular the tubular container constitutes the aforementioned guide tube and the object is the part that moves relative to that tube. The latter should consist of, or contain, a magnetic material at least at the point which is to serve for the detection of the position and orientation of the object relative to the container. That point could for instance be the forward end of the object.
An object of this type typically moves within the container so that the corresponding magnetic units can be advantageously mounted in an inside area of the container. On the other hand, if the moving object consists of a non-magnetic material while the container is provided with a magnetic element in an appropriate location, the corresponding magnetic units may equally well be mounted on an outside surface of the object. It is also possible, for facilitated access, to position the magnetic units on an outside surface of the container with the generated magnetic field extending through the wall and into the interior of the container.
In one possible, simple configuration for the precise capture of the moving object the magnetic units are arranged along at least one orientational plane perpendicular to the direction of relative movement. For example, multiple magnetic units may be arranged in a circular array or in some other way depending on the cross-sectional shape of the container, with the possibility of mounting the magnetic units, with equidistant spacing from one another, in the circumferential direction of the container.
So as not to limit the detection of the object to essentially one such plane, magnetic units may be mounted perpendicular to the direction of relative movement in evenly spaced planar increments. This permits capture in each of these staggered planes as well as detection between these planes by means of suitably interconnected magnetic units.
Depending on the design of the magnetic unit, it is possible for such a magnetic unit to be switchable between magnetic-field generation and magnetic-field sensing. This can take place even during the course of a measurement. Evidently, such switchability of the magnetic units involves variable polarity of the magnetic units, variable magnetic-field intensity or the like.
A simple design example of a magnetic-field-generating magnetic unit can be implemented in the form of a permanent magnet.
For an expanded range of possibilities in object detection per the above, a magnetic unit may be constituted of an electrically powered coil which provides a simple way to permit operation both for magnetic-field generation and magnetic-field measurement. A coil also allows for easy variation of the magnetic-field intensity or polarity and the generation of alternating fields.
A magnetic-field-measuring unit that is at once precise, simple and inexpensive may be in the form of a magnetic-field sensor and in particular a Hall element. Magnetic-field sensors of that type can be installed, in simple fashion and at low cost, in arrays of the desired density and configuration for instance on the inside of the container.
Of course, a suitably designed magnetic unit can also detect magnetic attenuation instead of measuring the magnetic field or magnetic flux.
For an amplification of the magnetic field and thus of the magnetic flux perpendicular to the direction of relative movement, the magnetic unit may incorporate a magnetizable material, for instance a ferromagnetic or paramagnetic material.
To avoid having to separately provide each magnetic unit with a magnetizable material, the magnetic units may be interconnected by a magnetizable or magnetically conductive material.
For a secure installation of the magnetic unit, the unit may be placed for instance in a radial bore in the container wall. The radial bore should be at least deep enough in the radial direction for the magnetic unit to be fully insertable without protruding into the interior of the container.
To avoid having to drill a corresponding number of radial bores or similar recesses in the container wall while at the same time being able to simultaneously manipulate a larger number of magnetic units, it is possible to mount multiple magnetic units in a magnetic-detector insert which may be mounted for instance in a circumferential recess on the inside of the container. This recess can again be deep enough to prevent the magnetic-detector insert with the magnetic units from protruding into the interior of the container.
Suitably designed magnetic units allow for the deployment in objects with a variety of cross sections. Of course, for oil exploration and similar applications it will be advantageous, and at the same time the data capture for the detection of the object within the container will be simplified, if the container and or object are essentially tubular in design. In applications related to oil and gas exploration, it is an essentially tubular object that is guided within an equally more or less tubular container. The object can be so guided that it is either in contact with or moves at a distance from the inside wall of the container.
In another possible, simple and space-saving design, a magnetic unit may be provided with a ramified and or continuous helical, electrically conductive ribbon. Such a ribbon essentially corresponds to a coil and generates a comparable magnetic field.
For the convenient manipulation of ribbon-shaped magnetic units of this type, the ribbon may be mounted on a preferably annular insert. The insert, of course, is shaped to correspond to the cross section of the container, permitting easy installation on an inside surface of the container.
The insert can allow for further simplification in that the necessary electrical power-supply and or signal-collecting leads are attached to the ribbon-shaped magnetic units mounted in the insert.
In analogous fashion it is possible in the case of the aforementioned magnetic-detector insert employing electrical coils to provide the electric coils with winding stems as magnetic units. The coils are wound on these winding stems which, like the entire magnetic-detector insert, may consist of a magnetizable material.
The evaluation especially of the signals received by the magnetic-field-sensing magnetic units is possible not only for determining the position of the object. A suitably equipped evaluation device may include a memory module and or a display unit or may be connectable to the latter or for instance to a computer. Stored in the memory module may be the necessary mathematical evaluation algorithms and/or address tags permitting the analysis of the measured signals. The display unit may be used, for example, for a graphic illustration of the object or for detecting the object.
The evaluation device may also be so configured that in addition to merely detecting the presence of the object it also permits the determination of the position, shape, size or direction of movement of the object.
The analysis of the signals emanating from the magnetic units and the very positioning of the magnetic units can be simplified for instance by aligning the magnetic axes of the magnetic units with a longitudinal axis of symmetry of the container.